1. Field of the Invention
The present invention relates generally to navigation systems and processes, and in particular to navigational deployment and initialization systems and methods, for use in connection with navigation-required environments and systems, including an inertial navigation-based system with multiple users navigating in a specified area or location.
2. Description of the Related Art
Inertial navigation systems are used and applied in various situations and environments that require accurate navigation functionality without the necessary use of external references during the navigational process. For example, inertial navigation systems and methods are used in many indoor environments (wherein a Global Navigation Satellite System, e.g., the Global Positioning System (GPS), is unusable or ineffective), such as in connection with the navigational activities of an emergency responder in a structure, building, or at a particular scene or location. However, in order to be effective, inertial navigation systems must initialize with estimate data, which may include data pertaining to the sensor position, velocity, orientation, biases, noise parameters, and other navigation-related data. In particular, for applications without external position or common azimuth references, a system must exist to correlate a personal inertial navigation module relative position output or series of relative position outputs (e.g., track) and relative azimuth with some reference (e.g., another user or track, structure, external reference, etc.).
Further, such as in pedestrian navigation applications, where each personal inertial navigation module is attached to a user (e.g., the boot of a firefighter), a system should relate the relative position of multiple users in the same frame of reference. For example, this relationship provides knowledge for one user to locate another user in the absence of external knowledge or aids. This further permits a command user to track multiple users navigating in the same environment. Following initialization and/or turn-on, inertial navigation systems require ongoing analysis and correction to mitigate drift, bias, noise, and other external factors that affect the accuracy of these sensors and systems.
Orientation determination is a requirement for most navigation systems. In certain existing systems, an Attitude Heading Reference System (AHRS) is implemented using gyroscopes that are updated with gravity sensors (pitch and roll) and magnetic field sensors (yaw), all having excellent long-term bias stability, i.e., minimal or no drift. However, the effective use of an AHRS in connection with low-cost inertial sensors requires computationally efficient and robust algorithms to initialize and account for sensor noise and bias drift. Accordingly, one important goal in inertial navigation-based navigation systems is the minimization or elimination of the bias drift, whether through improvement of the physical hardware or improvement of the algorithms and routines used during the navigational process.
Position is a requirement of most navigation systems. In certain existing systems, sensors may provide information relating to position, thereby allowing an algorithm to compute or derive position. In other systems, the sensor suite may not provide sufficient information to effectively derive position, and therefore may require an initial position estimate for which the system propagates thereafter. A user, device, marker, or other external source may provide such a position estimate. Of particular importance in first responder applications, e.g., emergency situation location and navigation, where the sensor suite may not provide sufficient information to effectively derive position, is the establishment of a single initial position estimate, whereby the navigation routines or algorithms initialize and place all users in a common frame of reference without any onerous procedural or physical requirements by the user. It is also recognized that location systems that provide or generate a graphical user path (such as at a central controller, e.g., an incident commander's computing device), require accurate track shape and relative track positioning between navigating users to improve situational awareness and accurate location management.
One known initialization and deployment approach uses one or more mats to establish a common coordinate system and heading between all firefighters. For example, such a system is at least partially described in U.S. Publication No. 2011/009821, the contents of which are incorporated herein by reference in their entirety. In such a single-mat approach, the mat may contain an array of markers that indicate the firefighter's horizontal sensor position relative to the mat's origin. As the firefighter walks across the mat, the boot-mounted inertial navigation module recognizes these inputs and aligns the module (and, thus, the user) coordinate system to match the coordinate system of the mat. A two-mat approach may also be used, where the relative position and orientation between each mat is arbitrary. In this arrangement, it is assumed that each mat represents one point, where the common coordinate system has the origin at the first mat and the x-axis extending from the first mat to the second mat. This provides a common heading or azimuth for each user.
It is recognized that certain situations or environments may not be amenable to a single- or two-mat-based solution. For example, following the deployment of the mats, these mats must remain stationary throughout the entire incident, such that all users initialize relative to the same reference, i.e., are positioned in a common navigation frame of reference. A small rotation or movement of a mat could result in significant horizontal error between those users initialized before and after this movement. In addition, the location or position of the mat must be consistent or its use for positioning the users in the common frame of reference will be altered or lost. Still further, these mats require precise location measurements for accurate azimuth alignment. The structure of the marker or mat may lead to issues based on mat size, mat weight, mat storage and transport, and deployment technique during the deployment process in an emergency situation. Effective deployment may require a substantially flat surface, where uneven ground will not allow the mat to lie flat, which may introduce other inaccuracies in the system. A convenient deployment location may not exist in the environment, and weather conditions may also affect or inhibit deployment.
As discussed above, it is important to understand the position of users relative to other users and/or other reference points or features navigating in or positioned at the location or scene. This allows for all users and various reference points or features to be placed in a common (e.g., global) frame of reference for accurate tracking. Accordingly, the processes for determining initial position and facilitating subsequent deployment of multiple users on or at the scene are critical for accurate tracking of the user in a common frame of reference. In addition, minimizing the user requirements to obtain and/or determine this initial position or location is beneficial.